A substrate processing apparatus may include a process space that, during operation, holds a gaseous atmosphere into and from which substrates may be inserted and extracted, respectively. The process space atmosphere may typically have characteristics that are different from those of an exterior atmosphere of the apparatus. The process space atmosphere may for example differ from the exterior atmosphere in chemical composition, temperature and/or pressure.
In case a process space atmosphere is maintained at a pressure that differs from that of the exterior atmosphere, any open connection between them is subject to a pressure differential that tends to drive atmospheric fluid from the atmosphere with the higher pressure, through the connection, towards the atmosphere with the lower pressure. Such a flow of atmospheric fluid may lead to contamination of the receiving atmosphere and to possible depletion of the supplying atmosphere. Furthermore, a substrate that is being exchanged between the exterior and the process space via the open connection is also subjected to the pressure differential. Although the pressure differential may be relatively small, it may still have a significant effect on the substrate. This is particularly so when the mass of the substrate is likewise small and the substrate is handled contactlessly (i.e. without mechanical contacts that restrain its motion).
To prevent the exterior atmosphere from mixing with the process space atmosphere, while at the same time enabling the exchange of substrates between them, the exterior may conventionally be connected to the process space via an air lock or a similar device. An air lock may provide for an intermediate space that can be selectively brought into communication with the exterior and the process space. Accordingly, a substrate may be exchanged between the exterior and the process space via the intermediate space, without bringing the exterior space and the process space in direct open communication with each other. By appropriately pressurizing the intermediate space, the air lock may also prevent the substrate from being subjected to the pressure differential, i.e. from being subjected to different pressures at different ends at the same time. However, air locks and the like have the drawback that they operate relatively slowly. This is partly due to their mechanical nature, and partly to the fact that their very design is aimed at the singular or batch-wise exchange of substrates between the exterior and the process space. As a result, the use of air locks may be accompanied by a detrimental effect on the through-put capacity of an apparatus. That is to say, the air lock may limit the rate at which substrates may be inserted into or extracted from the process space.
It is an object of the present invention to provide for an apparatus and a method that overcome or mitigate one or more of the above-mentioned problems, and that enable an open communication between an exterior and a process space comprising atmospheres at different pressures, which open communication allows substrates to be continuously exchanged between the exterior and the process space.